1. Field of the Disclosure
The present disclosure relates to an internal antenna, and more particularly, to an internal antenna, which may have a wideband characteristic in a device with a narrow space like a mobile communication terminal and ensure isolation and correlation of a multi input multi output (MIMO) system.
2. Description of the Related Art
In the wireless communication technology, as voice communication service is associated with high-quality multimedia service through a mobile terminal, fusion with a next-generation wireless communication service such as long term evolution (LTE) attracts great interest.
Generally, a communication system based on voice communication service uses a single input single output (SISO) system using a single antenna unit for the sake of a narrow-band channel within a limited frequency range. However, the SISO system using a single antenna may not easily transfer a large amount of data at a high speed in the narrow-band channel, and thus more advanced techniques are needed.
For this reason, there is needed a multiple input multiple output (MIMO) technique which is a next-generation wireless transmission technique capable of transmitting/receiving data faster with less errors by independently operating a plurality of antennas.
By using multiple antennas at transmitting and receiving terminals, the MIMO system may transmit data at a high speed without increasing the number of allocated frequencies used by the entire system, which allows efficient use of the limited frequency resources. The MIMO system is therefore widely used in the art.
However, in order to mount the MIMO antennas in an inner space of a slim mobile communication terminal, it is necessary to overcome deteriorated transmitting/receiving performance caused by mutual electromagnetic coupling or insufficient isolation among the mounted antennas.
In order to solve this problem, it may be conceived to install antennas spaced apart from each other by λ/2 or above (here, λ is a wavelength of radio waves emitted from the antennas). However, since a small antenna system has a limited space for antennas installed therein, it may be impossible to install antennas distantly from each other and thus the above problem cannot be solved.
Meanwhile, considering the recent trend of the antenna technology, a next-generation mobile communication system should have a plurality of antennas in a mobile communication terminal and use a low-frequency LTE band. Therefore, at least two MIMO antennas should be mounted in the terminal.
However, in order to support the low-frequency LTE band, an antenna having a wideband characteristic including the low-frequency band is required, and a sufficient ground as much as ¼ wavelength of the use frequency should be ensured. However, since a mobile communication terminal has a small size and a limited space, it is very difficult to satisfy such design requirements.
Therefore, in the technical field of the present disclosure, there is an urgent demand to develop an antenna technique which may ensure isolation and correlation of a MIMO system while having a wideband characteristic including a low-frequency band.